The regional cerebral perfusion has been studied by [15O]-butanol PET in bradykinetic patients with Parkinson's disease. In comparison with the rest condition significantly higher perfusion was detected in the primary sensorimotor cortex, parietal cortex, premotor cortex and supplementary motor area. A decrease of activity was observed in the lateral motor cortex, medial frontal cortex, dorsolateral prefrontal cortex and bilaterally in the head of the caudate nuclei. The method is capable of demonstrating the reorganisation of extrapyramidal movement regulation and the impact of medical and surgical treatment modalities. Based on the results conclusions can be drawn for the modes of action of the different treatment modalities.